function types
max.wolf
0.50.
I think it is a nice step forward.
Now i wonder if it would be a good idea to have type declarations for
functions as well.
Something like:
public factorial::number;
with the semantics that an exception is thrown by the runtime in case
the computed value doesn't match the type declaration.
Perhaps this could even render the "defined" pragma unnecessary.
Max
max.wolf
Albert Graef
Sorry for the late reply, I was somewhat busy over the holidays.
On 12/27/2011 11:29 PM, max.wolf wrote:
> It was a pleasent surprise to see "interfaces" introduced in pure
> 0.50.
> I think it is a nice step forward.
> Now i wonder if it would be a good idea to have type declarations for
> functions as well.
I left this out on purpose. For the purpose of defining a type via a
description of its interface, the result type of a function isn't really
needed anywhere.
> Something like:
>
> public factorial::number;
>
> with the semantics that an exception is thrown by the runtime in case
> the computed value doesn't match the type declaration.
A simple approach like this won't fly in Pure since many functions are
polymorphic. So we'd need to add a lot of syntactic baggage to the
language to just declare something like "this function returns type x if
applied to such and such arguments".
But there's already an easy way to get that with ordinary Pure code.
Just define yourself an 'assert' function, e.g., like this:
assert p x = if p x then x else throw (bad_assert p x);
Then you can write, e.g.,
factorial n = assert numberp (if n>0 then n*factorial (n-1) else 1);
An alternative would be to define 'assert' as a macro that could
conditionally be optimized away at compile time if not wanted, similar
to how C's 'assert' works:
//#! --disable assertions
#! --if assertions
def assert p x = if p y then y else throw (bad_assert p y) when y = x end;
#! --else
def assert p x = x;
#! --endif
Cheers,
Albert
--
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email: Dr.G...@t-online.de, a...@muwiinfa.geschichte.uni-mainz.de
WWW: http://www.musikinformatik.uni-mainz.de/ag